Liquid crystal display device using OCB mode and cholesteric liquid crystal color filter and fabricating method thereof

ABSTRACT

A liquid crystal display device includes first and second substrates having inner surfaces facing and spaced apart from each other; a light absorption layer on an inner surface of the first substrate; a cholesteric liquid crystal color filter (CCF) layer on the light absorption layer for selectively reflecting light corresponding to one of red, green, and blue colors; a first transparent electrode on the CCF layer; a first orientation film on the first transparent electrode; a second transparent electrode on the inner surface of the second substrate; a second orientation film on the second transparent electrode, the first and second orientation films being rubbed along the same direction; a polarizing plate on an outer surface of the second substrate; and a layer of liquid crystal material between the first and second orientation films, wherein the layer of liquid crystal material has a bend structure.

This application is a Divisional of prior application Ser. No.10/691,602, filed Oct. 24, 2003, now U.S. Pat. No. 7,057,688.

This application claims the benefit of Korean Patent Applications No.2002-67119, filed on Oct. 31, 2002, which is hereby incorporated byreference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to liquid crystal display (LCD) devices,and more particularly to an LCD device incorporating a cholestericliquid crystal color filter (CCF) layer.

2. Discussion of the Related Art

Due to their light weight, thin profile, and low power consumptioncharacteristics, LCD devices are currently being developed as nextgeneration display devices. Generally, LCD devices are non-emissive typedisplay devices capable of displaying images by exploiting anisotropicoptical refractive index difference properties of liquid crystalmaterial interposed between a thin film transistor (TFT) array substrateand a color filter (C/F) substrate. Among the various types of commonlyused LCD devices, active matrix LCD (AM-LCD) devices are capable ofdisplaying images at high resolution and are excellent at displayingmoving images.

Since LCD devices are non-emissive, one type of LCD device, thetransmissive LCD device, displays images using light emitted from anexternal light source (e.g., a backlight unit). The efficiency withwhich transmissive LCD devices transmit the light emitted from backlightunits, however, is relatively low. For example, only about 7% of thelight emitted from backlight units is actually transmitted bytransmissive LCD devices. Therefore, backlight units of transmissive LCDmust emit light at a relatively high intensity (brightness).Consequently, backlight units account for a relatively large percentageof all power consumed by transmissive LCD devices. Further, largecapacity batteries must typically be used to supply a sufficient amountof power to the backlight unit. However, even when large capacitybatteries are used, the operating times of transmissive LCD devicesbecome limited.

To solve the aforementioned problems related to transmissive LCDdevices, reflective LCD devices have been developed that do not requirebacklight units but, rather, use ambient light as a light source. Afirst type of reflective LCD device includes absorption type colorfilter layers and a reflective layer. A second type of reflective LCDdevice includes cholesteric liquid crystal color filter (CCF) layer forselectively reflecting and transmitting light. Accordingly, the CCFlayer in the second type of reflective LCD device functions both as acolor filter layer and as a reflective layer and enables the second typeof reflective LCD device to display images having high color purity.Moreover, since a separate reflective layer is not necessary, processesused to fabricate the second type of reflective LCD devices aresimplified compared to the first type of reflective LCD device.

Liquid crystal molecules within liquid crystal material exhibiting anematic liquid crystal phase are regularly aligned along one direction.CCF layers are formed from multiple layers of cholesteric liquid crystal(CLC) material exhibiting the nematic liquid crystal phase wherein arotation of liquid crystal molecules, and therefore reflectancecharacteristics, between the multiple layers of CLC material isdifferent. The difference in reflectance characteristics allow colors tobe selectively displayed by reflection and interference of the light.The rotation of liquid crystal molecules within CLC material generates ahelical structure that may be defined by a direction of the molecularrotation and a pitch (e.g., the distance between liquid crystalmolecules having the same alignment, measured along the axis ofrotation) of liquid crystal molecules within the CLC material. The pitchof the CLC material is variable and determines the wavelength of lightthe CLC material reflects. The central wavelength of light reflected bythe CLC material, λ_(c), can be expressed as the product of the pitch,p, of the CLC material and the average refractive index, n_(avg), of theCLC material (i.e., λ_(c)=n_(avg)·p). For example, if a pitch, p, of theCLC material is about 430 nm and an average refractive index of the CLCmaterial is about 1.5, the central wavelength of the reflected light isabout 650 nm and corresponds to the color red. CLC material capable ofreflecting green and blue light can similarly be provided by forming CLCmaterial to have the corresponding pitch.

FIG. 1 illustrates a cross-sectional view of a related art reflectiveliquid crystal display device incorporating a cholesteric liquid crystalcolor filter layer.

Referring to FIG. 1, first substrate 10 includes an inner surface thatfaces and is spaced apart from an inner surface of a second substrate50. A light absorption layer 12 is formed on the inner surface of thefirst substrate 10 and a cholesteric liquid crystal color filter (CCF)layer 14 is formed on the light absorption layer 12 for selectivelyreflecting light having predetermined wavelength range. The lightabsorption layer 12 absorbs light of all wavelengths except for thelight selectively reflected by the CCF layer 14. A first transparentelectrode 16 is formed on the CCF layer 14 and a first orientation film18 is formed on the first transparent electrode 16. An array elementlayer 52 is formed on the inner surface of the second substrate 50 and asecond transparent electrode 54 is formed on the array element layer 52.A second orientation film 56 is formed on the second transparentelectrode 54. A layer of liquid crystal material 70 is interposedbetween the first and second orientation films 18 and 56. A retardationfilm 60 is formed on an outer surface of the second substrate 50 and apolarizing plate 62 is formed on the retardation film 60.

Generally, a broadband quarter wave plate (QWP) having a retardationvalue of λ/4 or 3λ/4 is used as the retardation film 60 and changes apolarization state of light. For example, the broadband QWP convertscircularly polarized light into linearly polarized light, andvice-versa.

Although not shown in FIG. 1, the array element layer 52 generallyincludes a plurality of gate lines, a plurality of data lines crossingthe plurality of gate lines, and thin film transistors connected torespective ones of the gate and data lines at crossings of the gate anddata lines. Pixel regions are defined by crossings of the gate and datalines.

FIG. 2A schematically illustrates optical driving principles of arelated art reflective LCD device incorporating a CCF layer in theabsence of a voltage applied to a layer of liquid crystal material. FIG.2B schematically illustrates optical driving principles of a related artreflective LCD device incorporating a CCF layer in the presence of avoltage applied to a layer of liquid crystal material.

For convenience of illustration, the related art reflective LCD deviceshown in FIGS. 2A and 2B functions in a normally black mode (i.e., ablack image is displayed in the absence of an applied voltage). Further,for convenience of illustration, only a red sub pixel region is shown inFIGS. 2A and 2B.

Referring to FIGS. 2A and 2B, the polarizing plate 62 is provided as alinear polarizer having a polarization axis of 0° and the retardationfilm 60 is provided as a broadband quarter wave plate (QWP) capable ofaltering the phase of incident light by +45° and the phase of reflectedlight by −45°. In the absence of an applied voltage, the layer of liquidcrystal material 70 has a first retardation value of λ/2 and, in thepresence of an applied voltage, the layer of liquid crystal material 70has a second retardation value of 0. The layer of liquid crystalmaterial 70, first orientation film 18, and second orientation film 56(from FIG. 1) constitute a parallel cell and rubbing directions of thefirst and second orientation films 18 and 56 cross each other at anangle of 180°. The CCF layer 14 selectively reflects only left-handedcircularly polarized light having a wavelength corresponding to thecolor red.

Referring now to FIG. 2A, non-polarized ambient light incident to thepolarizing plate 62 becomes linearly polarized light in correspondencewith the polarization axis of the polarizing plate 62. Thus, linearlypolarized light having a polarizing angle of 0° is transmitted by thepolarizing plate 62 and is subsequently converted into left-handedcircularly polarized light by the retardation film 60. Since the layerof liquid crystal material 70 has the first retardation value of λ/2 inthe absence of an applied voltage (i.e., V=0; off state), theleft-handed circularly polarized light transmitted by the retardationfilm is converted into right-handed circularly polarized light by thelayer of liquid crystal material 70. Further, since the CCF layer 14selectively reflects only left-handed circularly polarized light havinga wavelength range corresponding to the color red, the right-handedcircularly polarized light is transmitted by the CCF layer 14 and isabsorbed by the light absorption layer 12. Accordingly, the reflectiveLCD device is maintained in a black state.

Referring now to FIG. 2B, non-polarized ambient light incident to thepolarizing plate 62 becomes linearly polarized light in correspondencewith the polarization axis of the polarizing plate 62. Thus, linearlypolarized light having a polarizing angle of 0°, transmitted by thepolarizing plate 62, is subsequently converted into left-handedcircularly polarized light by the retardation film 60. Since the layerof liquid crystal material 70 has the second retardation value of 0 inthe presence of the applied voltage of (i.e., V=V₀, wherein V₀ is theturn-on voltage of the layer of liquid crystal material 70), theleft-handed circularly polarized light transmitted by the retardationfilm is not converted by the layer of liquid crystal material 70.Further, since the CCF layer 14 selectively reflects only left-handedcircularly polarized light having a wavelength range corresponding tothe color red, red left-handed circularly polarized light transmitted bythe layer of liquid crystal material 70 is reflected by the CCF layer14. The reflected red left-handed circularly polarized light is thentransmitted by the layer of liquid crystal material 70 and issubsequently converted into red linearly polarized light having apolarizing angle of 0° by the retardation film 60. As the red linearlypolarized light transmitted by the retardation film 60 has thepolarizing angle of 0°, the red linearly polarized light is transmittedby the polarizing plate 62 having the polarizing angle of 0°. Theoptical driving principles described above with respect to red light aresimilarly applicable to wavelength ranges of light corresponding togreen and blue colors. Accordingly, the related art reflective LCDdevice maintains a white state by combining the reflected red, green,and blue light.

The related art reflective LCD device shown in FIGS. 1, 2A and 2B canalso be fabricated as a transmissive LCD device incorporating the CCFlayer. Accordingly, CCF layers capable of selectively reflectingwavelength ranges of light corresponding to green and blue colors areformed within the red sub pixel region such that only red light istransmitted by the CCF layers.

FIG. 3 illustrates a cross-sectional view of a related art transmissiveLCD device incorporating a CCF layer.

Referring to FIG. 3, first substrate 110 includes an inner surface thatfaces and is spaced apart from an inner surface of a second substrate150. A cholesteric liquid crystal color filter (CCF) layer 112,including first and second sub-CCF layers 112 a and 112 b, respectively,is formed on the inner surface of the first substrate 110. A firsttransparent electrode 114 is formed on the CCF layer 112 and a firstorientation film 116 is formed on the first transparent electrode 114. Afirst polarizing plate 120 is formed on an outer surface of the firstsubstrate 110. An array element layer 152 is formed on an inner surfaceof the second substrate 150 and a second transparent electrode 154 isformed on the array element layer 152. A second orientation film 156 isformed on the second transparent electrode 154. A retardation film 160is formed on an outer surface of the second substrate 150 and a secondpolarizing plate 162 is formed on the retardation film 160. The firstpolarizing plate 120 is formed of a cholesteric liquid crystal (CLC)material that selectively reflects left-handed or right-handedcircularly polarized light of all wavelengths (e.g., light of allcolors). The CCF layer 112 selectively reflects left-handed orright-handed circularly polarized light within a predeterminedwavelength range (i.e., light of a predetermined color). Accordingly,the first polarizing plate 120 and the CCF layer 112 are typically madeof different materials.

A layer of liquid crystal material 170 is interposed between the firstand second orientation films 116 and 156. The layer of liquid crystalmaterial 170, first orientation film 116, and second orientation film156 constitute a parallel cell an rubbing directions of the first andsecond orientation films 116 and 156 cross each other at an angle of180°. A backlight unit 180 is disposed beneath the first polarizingplate 120.

Although not shown in FIG. 3, the array element layer 152 generallyincludes a plurality of gate lines, a plurality of data lines crossingthe gate lines, and thin film transistors connected to respective onesof the gate and data lines at crossings of the gate and data lines.Pixel regions are defined by crossings of the gate and data lines.

FIG. 4A schematically illustrates optical driving principles of arelated art transmissive LCD device incorporating a CCF layer in theabsence of a voltage applied to a layer of liquid crystal material. FIG.4B schematically illustrates optical driving principles of a related arttransmissive LCD device incorporating a CCF layer in the presence of avoltage applied to a layer of liquid crystal material.

For convenience of illustration, the related art transmissive LCD deviceof FIGS. 4A and 4B functions in a normally black mode (i.e., a blackimage is displayed in the absence of an applied voltage). Further, forconvenience of illustration, only a red sub pixel region is shown inFIGS. 4A and 4B.

Referring to FIGS. 4A and 4B, the first polarizing plate 120 is formedof cholesteric liquid crystal (CLC) material that selectively reflectsonly right-handed circularly polarized light of all wavelengths (e.g.,all colors). The second polarizing plate 162 is provided as a linearpolarizer having a polarization axis of 0°. The retardation film 160 isprovided as a broadband quarter wave plate (QWP) capable of altering thephase of incident light by +45° and the phase of reflected light by−45°. The cholesteric liquid crystal color filter (CCF) layer 112includes first and second sub-CCF layers 112 a and 112 b thatselectively reflect left-handed circularly polarized light havingwavelengths within predetermined ranges corresponding to green and bluecolors, respectively. In the absence of an applied voltage, the layer ofliquid crystal material 170 has a first retardation value of λ/2 and, inthe presence of an applied voltage, the layer of liquid crystal material170 has a second retardation value of 0.

Referring now to FIG. 4A, of the non-polarized light emitted by thebacklight unit 180 and incident to the first polarizing plate 120,right-handed circularly polarized light of all wavelengths isselectively reflected and only left-handed circularly polarized light ofall wavelengths is transmitted by the first polarizing plate 120. TheCCF layer 112, including the first and second sub CCF layers 112 a and112 b, then selectively reflects only the incident left-handedcircularly polarized light having wavelength ranges corresponding togreen and blue colors. Accordingly, only left-handed circularlypolarized light having a wavelength range corresponding to the color redis transmitted by the CCF layer 112. Since the layer of liquid crystalmaterial 170 has the first retardation value of λ/2 in the absence of anapplied voltage (i.e., V=0; off state), the left-handed circularlypolarized light transmitted by the CCF layer 112 is converted intoright-handed circularly polarized by the layer of liquid crystalmaterial 170. The right-handed circularly polarized light is thenconverted into linearly polarized light having a polarizing angle of 90°via the retardation film 160. Since the second polarizing plate 162 is alinear polarizer having a polarization axis of 0°, the linearlypolarized light having a polarizing angle of 90° does not pass throughthe second polarizing plate 162. Accordingly, the transmissive LCDdevice is maintained in a black state.

Referring now to FIG. 4B, of the non-polarized light emitted by thebacklight unit 180 and incident to the first polarizing plate 120,right-handed circularly polarized light of all wavelengths isselectively reflected and only left-handed circularly polarized light ofall wavelengths is transmitted by the first polarizing plate 120. TheCCF layer 112, including the first and second sub CCF layers 112 a and112 b, then selectively reflects only the incident left-handedcircularly polarized light having wavelength ranges corresponding togreen and blue colors. Accordingly, only left-handed circularlypolarized light having a wavelength range corresponding to the color redis transmitted by the CCF layer 112. Since the layer of liquid crystalmaterial 170 has the second retardation value of 0 in the presence ofthe applied voltage (i.e., V=V₀; on state), the left-handed circularlypolarized light transmitted by the CCF layer 112 is also transmitted bythe layer of liquid crystal material 170. The left-handed circularlypolarized light is then converted into linearly polarized light having apolarizing angle of 0° via the retardation film 160. Since the secondpolarizing plate 162 is a linear polarizer having a polarization axis of0°, the linearly polarized light having a polarizing angle of 0° istransmitted by the second polarizing plate 162. The optical drivingprinciples described above with respect to red light are similarlyapplicable to wavelengths of light corresponding to green and bluecolors. Accordingly, the related art transmissive LCD device maintains awhite state by combining the transmitted red, green, and blue light.

As mentioned above, the related art LCD devices incorporating the CCFlayer use retardation films formed from a broadband QWP to displayimages. The broadband QWP compensates phase differences for broadbandwavelengths light (e.g., light of having wavelength ranges correspondingto red, green, and blue colors). Related art broadband QWPs generallyare constructed of a multi-layer system including a conventional QWP anda half wave plate (HWP). Accordingly, relatively large fabrication costsare associated with broadband QWPs and the reliability of LCD devicesincluding a broadband QWP becomes reduced due to shrinkage anddistortion problems inherent to broadband QWPs.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay device that substantially obviates one or more of problems dueto limitations and disadvantages of the related art.

An advantage of the present invention provides a liquid crystal displaydevice incorporating a cholesteric liquid crystal color filter (CCF)layer that does not incorporate a retardation film.

Another advantage of the present invention provides a liquid crystaldisplay device incorporating a CCF layer that is fabricated with a lowfabrication cost and a high production yield.

Yet another advantage of the present invention provides transmissive andreflective liquid crystal display devices incorporating CCF layers thatdo not include retardation films.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Otheradvantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a liquidcrystal display device may, for example, include first and secondsubstrates each having inner surfaces facing and spaced apart from eachother; a light absorption layer arranged on the inner surface of thefirst substrate; a cholesteric liquid crystal color filter (CCF) layerarranged on the light absorption layer, wherein the CCF layerselectively reflects light corresponding to a wavelength range of one ofred, green, and blue light; a first transparent electrode arranged onthe CCF layer; a first orientation film arranged on the firsttransparent electrode; a second transparent electrode arranged on theinner surface of the second substrate; a second orientation filmarranged on the second transparent electrode, wherein the first andsecond orientation films are rubbed along the same direction; apolarizing plate may be arranged on an outer surface of the secondsubstrate; and a layer of liquid crystal material arranged between thefirst and second orientation films, wherein the layer of liquid crystalmaterial has a bend structure.

In another aspect of the present invention, a liquid crystal displaydevice may, for example, include first and second substrates each havinginner surfaces facing and spaced apart from each other; a firstpolarizing plate arranged on an outer surface of the first substrate; acholesteric liquid crystal color filter (CCF) layer arranged on theinner surface of the first substrate, the CCF layer for selectivelytransmitting light corresponding to wavelengths of one of red, green,and blue light; a first transparent electrode arranged on the CCF layer;a first orientation film arranged on the first transparent electrode; asecond transparent electrode arranged on the inner surface of the secondsubstrate; a second orientation film arranged on the second transparentelectrode, wherein the first and second orientation films are rubbedalong one direction; a second polarizing plate arranged on an outersurface of the second substrate; a layer of liquid crystal materialarranged between the first and second orientation films, wherein thelayer of liquid crystal material has a bend structure; and a backlightunit arranged beneath the first polarizing plate.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included herewith to provide afurther understanding of the invention and are incorporated in andconstitute a part of this specification, illustrate embodiments of theinvention and together with the description serve to explain theprinciple of the invention.

In the drawings:

FIG. 1 illustrates a cross-sectional view of a related art reflectiveliquid crystal display device incorporating a cholesteric liquid crystalcolor filter (CCF) layer;

FIG. 2A schematically illustrates optical driving principles of arelated art reflective LCD device incorporating a CCF layer in theabsence of a voltage applied to a layer of liquid crystal material;

FIG. 2B schematically illustrates optical driving principles of arelated art reflective LCD device incorporating a CCF layer in thepresence of a voltage applied to a layer of liquid crystal material;

FIG. 3 illustrates a cross-sectional view of a related art transmissiveLCD device incorporating a CCF layer;

FIG. 4A schematically illustrates optical driving principles of arelated art transmissive LCD device incorporating a CCF layer in theabsence of a voltage applied to a layer of liquid crystal material;

FIG. 4B schematically illustrates optical driving principles of arelated art transmissive LCD device incorporating a CCF layer in thepresence of a voltage applied to a layer of liquid crystal material;

FIG. 5 illustrates an optically compensated birefringence mode liquidcrystal display device according to the principles of the presentinvention;

FIG. 6 illustrates a cross-sectional view of a reflective liquid crystaldisplay device incorporating a CCF layer in accordance with a firstaspect of the present invention;

FIG. 7 illustrates a cross-sectional view of an array element layerwithin one sub-pixel region of a reflective liquid crystal displaydevice incorporating a CCF layer in accordance with the first aspect ofthe present invention;

FIG. 8A schematically illustrates optical driving principles of areflective liquid crystal display device shown in FIG. 6 in the presenceof a minimum voltage applied to a layer of liquid crystal material;

FIG. 8B schematically illustrates optical driving principles of areflective liquid crystal display device shown in FIG. 6 in the presenceof a maximum voltage applied to a layer of liquid crystal material;

FIG. 9 illustrates a cross-sectional view of a transmissive liquidcrystal display device incorporating a CCF layer in accordance with asecond aspect of the present invention;

FIG. 10A schematically illustrates optical driving principles of atransmissive liquid crystal display device shown in FIG. 9 in thepresence of a minimum voltage applied to a layer of liquid crystalmaterial; and

FIG. 10B schematically illustrates optical driving principles of atransmissive liquid crystal display device shown in FIG. 9 in thepresence of a maximum voltage applied to a layer of liquid crystalmaterial.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the illustrated embodiments ofthe present invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, similar reference numbers willbe used throughout the drawings to refer to the same or like parts.

Liquid crystal display (LCD) devices manipulate electro-opticalcharacteristics of a layer of liquid crystal material to display images.Accordingly, voltages applied to the layer of liquid crystal materialmay be adjusted to control light transmittance characteristics of thelayer of liquid crystal material. LCD devices may generally beclassified into three types: current-effect type; electric field-effecttype; and heat-effect type LCD devices.

Electric field-effect type LCD devices operate in one of a twistednematic (TN) mode, a guest-host (GH) mode, an electrically controlledbirefringence (ECB) mode, and a phase change mode. Within ECB mode LCDdevices, a uniformly oriented layer of liquid crystal material isinterposed between orthogonally aligned polarizers. Light transmittancecharacteristics of the layer of liquid crystal material may be alteredaccording to a birefringence effect induced by applied voltages. Of thetypes ECB mode LCD devices, a substantially symmetric bend structure maybe induced within liquid crystal (LC) molecules of optically compensatedbirefringence (OCB) mode LCD devices, wherein an angle defined betweenthe long axis of LC molecules present midway between opposing substratesof an OCB mode LCD device and the long axis of LC molecules adjacent thesubstrates is substantially 90°, and wherein the angle between the longaxes gradually decreases moving away from the midpoint, toward thesubstrates. Due to the substantially symmetric bend structure, OCB modeLCD devices generally have low response times.

FIG. 5 illustrates an OCB mode LCD device according to the principles ofthe present invention.

Referring to FIG. 5, first and second substrates 130 and 140,respectively, each include inner surfaces facing and spaced apart fromeach other. A layer of liquid crystal material 134 may be interposedbetween the first and second substrates 130 and 140. First and secondpolarizing plates 136 and 138, respectively, may be formed on outersurfaces of the first and second substrates 130 and 140, respectively. Afirst orientation film (not shown) may be formed between the innersurface of the first substrate 130 and the layer of liquid crystalmaterial 134 while a second orientation film (not shown) may be formedbetween the inner surface of the second substrate 140 and the layer ofliquid crystal material 134. In one aspect of the present invention, thealignment direction of the first and second orientation films may besubstantially the same. In another aspect of the present invention, thefirst and second orientation films may be rubbed along the samedirection. According to the principles of the present invention, thelayer of liquid crystal material 134, the first orientation film, andthe second orientation films constitute a bend cell having theaforementioned bend structure in the presence of an applied voltagegreater than a threshold voltage of the layer of liquid crystal material134.

In the presence of the applied voltage, liquid crystal molecules withinthe layer of liquid crystal material 134 may quickly rotate. In oneaspect of the present invention, the time required to realign the liquidcrystal molecules (i.e., response time) may be less than about 5milliseconds. Accordingly, the OCB mode LCD device of the presentinvention may be provided with a response time sufficient tosubstantially eliminate residual images and therefore capable ofdisplaying moving images. In another aspect of the present invention,while the OCB mode LCD device may have an adequate response time, aviewing angle may be relatively narrow. Thus, the viewing angle may bewidened using a compensating film (not shown) provided as a biaxial filmhaving a simpler structure than a retardation film and be fabricatedaccording to a simpler process than that required to fabricate aretardation film. Further, the material cost of the compensating filmmay be substantially less than that of the retardation film. In oneaspect of the present invention, the compensating film may be interposedbetween the outer surface of the second substrate 140 and the secondpolarizing plate 138. Accordingly, retardation films such as thoseincorporated within the aforementioned related art LCD devices are notrequired by the LCD device of the present invention.

According to the principles of the present invention, the layer ofliquid crystal material 134 may be driven between a minimum voltage anda maximum voltage. In one aspect of the present invention, the maximumvoltage may be greater than a threshold voltage of the layer of liquidcrystal material. In one aspect of the present invention, the minimumvoltage may be substantially equal to the threshold voltage of the layerof liquid crystal material required to induce the aforementioned bendstructure. In another aspect of the present invention, the layer ofliquid crystal material 134 may have a first retardation value of 3λ/4in the presence of the applied minimum voltage and a second retardationvalue of λ/4 in the presence of the applied maximum voltage.

FIG. 6 illustrates a cross-sectional view of a reflective liquid crystaldisplay device incorporating a CCF layer in accordance with a firstaspect of the present invention.

Referring to FIG. 6, first and second substrates 210 and 250,respectively, may each include inner surfaces facing and spaced apartfrom each other. A light absorption layer 212 may be formed on the innersurface of the first substrate 210 and a cholesteric liquid crystalcolor filter (CCF) layer 214 may be formed on the light absorption layer212. The light absorption layer 212 may be formed of a black resin. TheCCF layer 214 may selectively reflect light having a predeterminedwavelength range. The light absorption layer 212 may absorb light of allwavelengths except for the light selectively reflected by the CCF layer214. A first transparent electrode 216 may be formed on the CCF layer214 and a first orientation film 218 may be formed on the firsttransparent electrode 216. An array element layer 252 may be formed onthe inner surface of the second substrate 250 and a second transparentelectrode 270 may be formed on the array element layer 252. A secondorientation film 272 may be formed on the second transparent electrode270. A compensating layer 280 may be formed on an outer surface of thesecond substrate 250 and a polarizing plate 282 may be formed on thecompensating film 280. A layer of liquid crystal material 290 may beinterposed between the first and second orientation films 218 and 272.

According to the principles of the present invention, the alignmentdirection of the first and second orientation films 218 and 272 may besubstantially the same. In one aspect of the present invention, thefirst and second orientation films 218 and 272 may be rubbed along thesame direction. The layer of liquid crystal material 290, the firstorientation film 218, and the second orientation film 272 may constitutea bend cell having the aforementioned bend structure in the presence ofan applied voltage that is greater than a threshold voltage of the layerof liquid crystal material 290. In another aspect of the presentinvention, the layer of liquid crystal material 290 may have a firstretardation value of 3λ/4 in the presence of the applied minimum voltageand a second retardation value of λ/4 in the presence of the appliedmaximum voltage. In one aspect of the present invention, the maximumvoltage may be greater than a threshold voltage of the layer of liquidcrystal material. In one aspect of the present invention, the minimumvoltage may be substantially equal to the threshold voltage of the layerof liquid crystal material to induce the aforementioned bend structure.

The compensating layer 280 of the present invention differs from theretardation film 60 shown in FIG. 1 because the compensating layer 280may be provided as a biaxial film having a simpler structure than theretardation film 60 shown in FIG. 1 and be fabricated according to asimpler process than that required to fabricate the retardation film 60.Further, the material cost of the compensating film may be substantiallyless than that of the retardation film. Accordingly, the compensatingfilm may widen the viewing angle and improve the display quality of theLCD device shown in FIG. 6 whereas the retardation film 60 of FIG. 1 isprovided as a broadband QWP that compensates a phase difference ofincident light. Accordingly, retardation films such as thoseincorporated within the aforementioned related art LCD devices are notrequired by the LCD device of the present invention. In one aspect ofthe present invention, the compensating layer 280 may be omitted byadjusting a parameter of the bend cell structure.

FIG. 7 illustrates a cross-sectional view of an array element layerwithin one sub-pixel region of a reflective liquid crystal displaydevice incorporating a CCF layer in accordance with the principles ofthe present invention.

Referring to FIG. 7, first and second substrates 210 and 250,respectively, each include inner surfaces facing and spaced apart fromeach other. A light absorption layer 212, a CCF layer 214, a firsttransparent electrode 216, and a first orientation film 218 aresequentially formed on the inner surface of the first substrate 210. Agate electrode 254 may be formed on the inner surface of the secondsubstrate 250 followed by the formation of a gate insulating layer 256on the gate electrode 254. Next, a semiconductor layer 258 may be formedover the gate insulating layer 256 and the gate electrode 254 followedby the formation of source and drain electrodes 260 and 262,respectively, on the semiconductor layer 258. In one aspect of thepresent invention, the source and drain electrodes 260 and 262 may bespaced apart from each other by a predetermined distance. A passivationlayer 266 may next be formed over the source and drain electrodes 260and 262. Further, a drain contact hole 264 may be formed within thepassivation layer 266 to expose the drain electrode 262. A secondtransparent electrode 270 may subsequently be formed over thepassivation layer 266 and be electrically connected to the drainelectrode 262 via the drain contact hole 264. Next, a second orientationfilm 272 may be formed over the second transparent electrode 270. Takentogether, the gate electrode 254, the semiconductor layer 258, thesource electrode 260, and drain electrode 262 constitute a thin filmtransistor (TFT) “T.”

Although not shown in FIG. 7, a gate line and a data line, crossing thegate line, may be formed over the inner surface of the second substrate250 to be connected to the gate electrode 254 and source electrode 260,respectively. Taken together, the gate and data lines and the TFT “T”constitute the array element layer 252. Upon applying a voltage to thefirst and second transparent electrodes 216 and 270, the layer of liquidcrystal material 290 may be driven, wherein the first transparentelectrode 216 acts as a common electrode and the second transparentelectrode 270 acts as a pixel electrode.

FIG. 8A schematically illustrates optical driving principles of areflective liquid crystal display device incorporating a CCF layer inthe presence of a minimum voltage applied to a layer of liquid crystalmaterial, and FIG. 8B schematically illustrates optical drivingprinciples of a reflective liquid crystal display device incorporating aCCF layer in the presence of a maximum voltage applied to a layer ofliquid crystal material.

For convenience of illustration, the reflective LCD device shown inFIGS. 8A and 8B may function in a normally black mode (i.e., a blackimage may be displayed in the presence of an applied minimum voltage).Further, for convenience of illustration, only a red sub-pixel region isshown in FIGS. 8A and 8B. It will be readily appreciated, however, thatthe optical driving principles described below may be similarly applied,for example, to green and blue sub-pixel regions as well.

Referring to FIGS. 8A and 8B, the polarizing plate 282 may be providedas a linear polarizer having a polarization axis of about 0°. Thecompensating layer 280 may be provided as a biaxial film for widening aviewing angle and improving a display quality of the reflective LCDdevice incorporating the cholesteric liquid crystal color filter (CCF)layer 214. The CCF layer 214 may selectively reflect only left-handedcircularly polarized light having a wavelength range corresponding tothe color red. The layer of liquid crystal material 290 may be providedto exhibit a bend structure in the presence of an applied voltagegreater than a threshold voltage. In one aspect of the presentinvention, the layer of liquid crystal material 290 may be drivenbetween a minimum voltage and a maximum voltage. In one aspect of thepresent invention, the maximum voltage may be greater than a thresholdvoltage of the layer of liquid crystal material. In one aspect of thepresent invention, the minimum voltage may be substantially equal to thethreshold voltage of the layer of liquid crystal material required toinduce the aforementioned bend structure. In another aspect of thepresent invention, the layer of liquid crystal material 290 may have afirst retardation value of 3λ/4 in the presence of the applied minimumvoltage and a second retardation value of λ/4 in the presence of theapplied maximum voltage. The layer of liquid crystal material 290, thefirst orientation film 218, and the second orientation film 272 mayconstitute a bend cell having the aforementioned bend structure in thepresence of an applied voltage greater than a threshold voltage of thelayer of liquid crystal material 290. In one aspect of the presentinvention, the alignment direction of the first and second orientationfilms 218 and 272 may be substantially the same. In another aspect ofthe present invention, the first and second orientation films 218 and272 may be rubbed along the same direction.

Referring now to FIG. 8A, non-polarized ambient light incident to thepolarizing plate 282, may become linearly polarized light incorrespondence with the polarization axis of the polarizing plate 282.Thus, linearly polarized light having a polarizing angle of about 0° maybe transmitted by the polarizing plate 282 become incident to the layerof liquid crystal material 290. Since the layer of liquid crystalmaterial 290 has the first retardation value of 3λ/4 in the presence ofthe applied minimum voltage (i.e., V=V_(min); the threshold voltage),the linearly polarized light having the polarizing angle of about 0° maybe converted into right-handed circularly polarized light by the layerof liquid crystal material 290. Further, since the CCF layer 214selectively reflects only left-handed circularly polarized light havinga wavelength range corresponding to the color red, the right-handedcircularly polarized light transmitted by the layer of liquid crystalmaterial 290 may also be transmitted by the CCF layer 214 and beabsorbed by a light absorption layer 212. Accordingly, the reflectiveLCD device may be maintained in a black state.

Referring now to FIG. 8B, non-polarized ambient light incident to thepolarizing plate 282 may become linearly polarized light incorrespondence with the polarization axis of the polarizing plate 282.Thus, linearly polarized light having a polarizing angle of about 0° maybe transmitted by the polarizing plate 282 and become incident to thelayer of liquid crystal material 290. Since the layer of liquid crystalmaterial 290 has the second retardation value of λ/4 in the presence ofthe applied maximum voltage (i.e., V=V_(max)), the linearly polarizedlight having the polarizing angle of about 0° may be converted intoleft-handed circularly polarized light by the layer of liquid crystalmaterial 290. Further, since the CCF layer 214 may reflect onlyleft-handed circularly polarized light having a wavelength rangecorresponding to the color red, only the red left-handed circularlypolarized light transmitted by the layer of liquid crystal material 290may be reflected by the CCF layer 214. The reflected left-handedcircularly polarized light having the wavelength corresponding to thecolor red may then be re-transmitted by the layer of liquid crystalmaterial 290 where it may subsequently be converted into red linearlypolarized light having a polarizing angle of about 0°. Since the redlinearly polarized light having the polarizing angle of about 0°substantially corresponds with the polarization axis of the polarizingplate 282, the red linearly polarized light having the polarizing angleof about 0° may be transmitted by the polarizing plate 282. The opticaldriving principles described above with respect to red light aresimilarly applied to green and blue light. Accordingly, the reflectiveLCD device of the present invention may maintain a white state bycombining the reflected red, green, and blue light.

In one aspect of the present invention, the aforementioned minimumvoltage may be between about 0.1 V and about 1.5 V. In another aspect ofthe present invention, the maximum voltage may be between about 4.0 Vand about 5.0 V. In yet another aspect of the present invention, theminimum and maximum voltages that may be applied to the layer of liquidcrystal material 290 may vary according to specific parameters of thelayer of liquid crystal material 290.

According to the principles of the present invention, the response timeand viewing angle characteristics of the reflective LCD device shown inFIG. 6 may be improved compared to the aforementioned related artreflective LCD device shown in FIG. 1. Further, use of retardation filmssuch as a broadband quarter wave plates (QWP) may be replaced using alayer of liquid crystal material having retardation values of 3λ/4 andλ/4.

FIG. 9 illustrates a cross-sectional view of a transmissive liquidcrystal display device incorporating a CCF layer in accordance with asecond aspect of the present invention.

Referring to FIG. 9, first and second substrates 310 and 350,respectively, each may include inner surfaces facing and spaced apartfrom each other. A cholesteric liquid crystal color filter (CCF) layer312 including first and second sub CCF layers 312 a and 312 b,respectively, may be formed on the inner surface of the first substrate310. A first transparent electrode 314 may be formed on the CCF layer312 and a first orientation film 316 may be formed on the firsttransparent electrode 314. A first polarizing plate 320 may be formed onan outer surface of the first substrate 310. An array element layer 352may be formed on the inner surface of the second substrate 350 and asecond transparent electrode 354 may be formed on the array elementlayer 352. A second orientation film 356 may be formed on the secondtransparent electrode 354. A compensating layer 360 may be formed on anouter surface of the second substrate 350 and a second polarizing plate362 may be formed on the compensating layer 360. A backlight unit 380may be disposed beneath the first polarizing plate 320. A layer ofliquid crystal material 390 may be interposed between the first andsecond orientation films 316 and 356.

As similarly described above with respect to FIGS. 5 and 6, the layer ofliquid crystal material 390, the first orientation film 316, and thesecond orientation film 356 may constitute a bend cell having a bendstructure in the presence of an applied voltage greater than a thresholdvoltage of the layer of liquid crystal material 390. Further, thecompensating layer 360 of the present invention differs from theretardation film 60 shown in FIG. 1 because the compensating layer 360may be provided as a biaxial film having a simpler structure than theretardation film 60 shown in FIG. 1 and be fabricated according to asimpler process than that required to fabricate the retardation film 60.Further, the material cost of the compensating film may be substantiallyless than that of the retardation film. Accordingly, the compensatingfilm may widen the viewing angle and improve the display quality of theLCD device shown in FIG. 9 whereas the retardation film 60 of FIG. 1 isprovided as a broadband QWP that compensates a phase difference ofincident light. Accordingly, retardation films such as thoseincorporated within the aforementioned related art LCD devices are notrequired by the LCD device of the present invention. In one aspect ofthe present invention, the compensating layer 360 maybe omitted byadjusting a parameter of the bend cell structure.

According to the second aspect of the present invention, the firstpolarizing plate 320 may be formed of a cholesteric liquid crystal (CLC)material capable of selectively reflecting only left-handed orright-handed circularly polarized light of all wavelengths. The CCFlayer 312 may be provided as a material capable of selectivelyreflecting only left-handed or right-handed circularly polarized lighthaving a predetermined wavelength range (i.e., color). According to theprinciples of the present invention, the first sub-CCF layer 312 a mayselectively reflect only left-handed or right-handed circularlypolarized light having a wavelength range corresponding to one of red,green, and blue colors while the second sub-CCF layer 312 b mayselectively reflect only left-handed or right-handed circularlypolarized light having a wavelength range corresponding to a differentone of the red, green, and blue colors. For example, within a redsub-pixel region, the first sub-CCF layer 312 a may selectively reflectonly left-handed circularly polarized light having a wavelengthcorresponding the color green while the second sub-CCF layer 312 b mayselectively reflect only left-handed circularly polarized light having awavelength corresponding to the color blue. Therefore, within the redsub-pixel region, only left-handed circularly polarized light having awavelength corresponding to the color red may be transmitted by the CCFlayer 312.

According to the principles of the present invention, the layer ofliquid crystal material 390 may be driven between a minimum voltage anda maximum voltage. In one aspect of the present invention, the maximumvoltage may be greater than a threshold voltage of the layer of liquidcrystal material. In one aspect of the present invention, the minimumvoltage may be substantially equal to the threshold voltage of the layerof liquid crystal material required to induce the aforementioned bendstructure. In another aspect of the present invention, the layer ofliquid crystal material 390 may have a first retardation value of 3λ/4in the presence of the applied minimum voltage and a second retardationvalue of λ/4 in the presence of the applied maximum voltage.Accordingly, retardation films such as those incorporated within theaforementioned related art LCD devices are not required by the LCDdevice of the present invention.

FIG. 10A schematically illustrates optical driving principles of atransmissive liquid crystal display device incorporating a CCF layer inthe presence of a minimum voltage applied to a layer of liquid crystalmaterial, and FIG. 10B schematically illustrates optical drivingprinciples of a transmissive liquid crystal display device incorporatinga CCF layer in the presence of a maximum voltage applied to a layer ofliquid crystal material.

For convenience of illustration, the transmissive LCD device shown inFIGS. 10A and 10B may function in a normally black mode (i.e., a blackimage may be displayed in the presence of an applied minimum voltage).Further, for convenience of illustration, only a red sub-pixel region isshown in FIGS. 10A and 10B. It will be readily appreciated, however,that the optical driving principles described below may be similarlyapplied, for example, to green and blue sub-pixel regions as well.

Referring to 10A and 10B, the first polarizing plate 320 may be providedas a cholesteric liquid crystal (CLC) material that selectively reflectsonly right-handed circularly polarized light for all wavelengths. Thecompensating layer 360 may be provided as a biaxial film for widening aviewing angle and improving a display quality of the transmissive LCDdevice incorporating the cholesteric liquid crystal color filter (CCF)layer 312. According to the principles of the present invention, thecompensating layer 360 may not change the phase of light and may beomitted by adjusting a parameter of the bend cell. The cholestericliquid crystal color filter (CCF) layer 312 may, for example, includefirst and second sub-CCF layers 312 a and 312 b, respectively, forreflecting only left-handed circularly polarized light havingwavelengths corresponding to green and blue colors, respectively. Thelayer of liquid crystal material 390 may be provided to exhibit a bendstructure in the presence of an applied voltage greater than a thresholdvoltage. In one aspect of the present invention, the layer of liquidcrystal material 390 may be driven between a minimum voltage and amaximum voltage. In one aspect of the present invention, the maximumvoltage may be greater than a threshold voltage of the layer of liquidcrystal material. In one aspect of the present invention, the minimumvoltage may be substantially equal to the threshold voltage of the layerof liquid crystal material required to induce the aforementioned bendstructure. In another aspect of the present invention, the layer ofliquid crystal material 390 may have a first retardation value of 3λ/4in the presence of the applied minimum voltage and a second retardationvalue of λ/4 in the presence of the applied maximum voltage. The secondpolarizing plate 362 may be provided as a linear polarizer having apolarization axis of about 0°.

Referring now to FIG. 10A, of the non-polarized light emitted by thebacklight unit 380 and incident to the first polarizing plate 320,right-handed circularly polarized light may be selectively reflectedsuch and only left-handed circularly polarized light of all wavelengthsmay be transmitted by the first polarizing plate 320. The CCF layer 312,including the first and second sub CCF layers 312 a and 312 b, then mayselectively reflect only the incident left-handed circularly polarizedlight having wavelength ranges corresponding to green and blue colors.Accordingly, only left-handed circularly polarized light having awavelength range corresponding to the color red may be transmitted bythe CCF layer 312. Since the layer of liquid crystal material 390 hasthe first retardation value of 3λ/4 in the presence of the appliedminimum voltage (i.e., V=V_(min); the threshold voltage), theleft-handed circularly polarized light having the wavelength rangecorresponding to the color red may be converted into red linearlypolarized light having a polarizing angle of about 90° via the layer ofliquid crystal material 390. Further, since the second polarizing plate362 may be provided as a linear polarizer having a polarization axis ofabout 0°, the red linearly polarized light having the polarizing angleof about 90° may not be transmitted by the second polarizing plate 362.Accordingly, the transmissive LCD device may be maintained in a blackstate.

Referring now to FIG. 10B, of the non-polarized light emitted by thebacklight unit 380 and incident to the first polarizing plate 320,right-handed circularly polarized light of all wavelengths may beselectively reflected and only left-handed circularly polarized light ofall wavelengths may be transmitted by the first polarizing plate 320.The CCF layer 312, including the first and second sub CCF layers 312 aand 312 b, may then selectively reflect the incident left-handedcircularly polarized light having wavelength ranges corresponding togreen and blue colors. Accordingly, only left-handed circularlypolarized light having a wavelength range corresponding to the color redmay be transmitted by the CCF layer 312. Since the layer of liquidcrystal material 390 has the second retardation value of λ/4 in thepresence of the applied maximum voltage (i.e., V=V_(max)), the liquidcrystal layer 390 may convert the left-handed circularly polarized lighttransmitted by the CCF layer 312 into red linearly polarized lighthaving a polarizing angle of about 0°. Further, since the secondpolarizing plate 362 is provided as a linear polarizer having apolarization axis of about 0°, red linearly polarized light having thepolarizing angle of about 0° may be transmitted by the second polarizingplate 362. The optical driving principles described above with respectto red light may be similarly applied to wavelengths of lightcorresponding to green and blue colors, or other colors. Accordingly,the transmissive LCD device of the present invention may maintain awhite state by combining the reflected red, green, and blue light.

The reflective and transmissive LCD devices of the present invention mayincorporate a layer of liquid crystal material having retardation valuessubstantially identical to those of related art broadband QWPretardation plates (e.g., 3λ/4 and λ4). Accordingly, the LCD devices ofthe present invention may maintain black and white states without theuse of the aforementioned related broadband QWP retardation films. Sincesuch related art retardation films are not used, problems related todevice reliability due to shrinkage and distortion of retardation filmsmay be avoided. Moreover, response time and viewing anglecharacteristics of the LCD device of the present invention may beimproved over the aforementioned related art LCD devices.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the method of manufacturinga liquid crystal display device of the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A liquid crystal display device, comprising: first substrate havingan inner surface.
 2. A liquid crystal display device, comprising: firstsubstrate having an inner surface; second substrate having an innersurface, wherein the inner surface of the second substrate faces and isspaced apart from the inner surface of the first substrate; a firstpolarizing plate arranged on an outer surface of the first substrate; acholesteric liquid crystal color filter (CCF) layer arranged on theinner surface of the first substrate, wherein the CCF layer selectivelytransmits light having a wavelength range corresponding to one of red,green, and blue colors; a first transparent electrode arranged directlyon the CCF layer; a first orientation film arranged on the firsttransparent electrode; a second transparent electrode arranged on theinner surface of the second substrate; a second orientation filmarranged on the second transparent electrode, wherein the first andsecond orientation films have substantially the same orientationdirections; a second polarizing plate arranged on an outer surface ofthe second substrate; a layer of liquid crystal material arrangedbetween the first and second orientation films, wherein the layer ofliquid crystal material includes a plurality of liquid crystal moleculeshaving a substantially symmetrical orientation about a mid-point betweenthe first and second orientation films, wherein the layer of liquidcrystal material functions in an optically compensated birefringence(OCB) mode and the plurality of liquid crystal molecules have thesubstantially symmetrical orientation in the presence of a voltageapplied to the layer of liquid crystal material, wherein the appliedvoltage is between a minimum voltage and a maximum voltage, and whereinthe layer of liquid crystal material has a retardation value of 3 λ/4when the applied voltage is substantially equal to the minimum voltage;and a backlight unit arranged under the first polarizing plate.
 3. Thedevice according to claim 2, wherein the first polarizing plate includescholesteric liquid crystal (CLC) material for selectively reflecting oneof left-handed and right-handed circularly polarized light of allwavelengths.
 4. The device according to claim 2, wherein the secondpolarizing plate includes a linear polarizer.
 5. The device according toclaim 2, further comprising: an array element layer arranged over theinner surface of the second substrate, wherein the array element layerincludes: a gate line; a data line crossing the gate line; and thin filmtransistor connected to the gate line and the data line.
 6. The deviceaccording to claim 5, wherein the array element layer is arrangedbetween the inner surface of the second substrate and the secondtransparent electrode.
 7. The device according to claim 2, furthercomprising a compensating film arranged between the outer surface of thesecond substrate and the second polarizing plate.
 8. The deviceaccording to claim 2, wherein the maximum voltage is greater than athreshold voltage of the layer of liquid crystal material. secondsubstrate having an inner surface, wherein the inner surface of thesecond substrate faces and is spaced apart from the inner surface of thefirst substrate; a first polarizing plate arranged on an outer surfaceof the first substrate; a cholesteric liquid crystal color filter (CCF)layer arranged on the inner surface of the first substrate, wherein theCCF layer selectively transmits light having a wavelength rangecorresponding to one of red, green, and blue colors; a first transparentelectrode arranged directly on the CCF layer; a first orientation filmarranged on the first transparent electrode; a second transparentelectrode arranged on the inner surface of the second substrate; asecond orientation film arranged on the second transparent electrode,wherein the first and second orientation films have substantially thesame orientation directions; a second polarizing plate arranged on anouter surface of the second substrate; a layer of liquid crystalmaterial arranged between the first and second orientation films,wherein the layer of liquid crystal material includes a plurality ofliquid crystal molecules having a substantially symmetrical orientationabout a mid-point between the first and second orientation films,wherein the layer of liquid crystal material functions in an opticallycompensated birefringence (OCB) mode and the plurality of liquid crystalmolecules have the substantially symmetrical orientation in the presenceof a voltage applied to the layer of liquid crystal material, whereinthe applied voltage is between a minimum voltage and a maximum voltage,and wherein the layer of liquid crystal material has a retardation valueof λ/4 when the applied voltage is substantially equal to the maximumvoltage; and a backlight unit arranged under the first polarizing plate.9. The device according to claim 2, wherein the minimum voltage issubstantially equal to a threshold voltage of the layer of liquidcrystal material.
 10. The device according to claim 2, wherein theminimum voltage is between about 1.0 V and about 1.5 V.
 11. The deviceaccording to claim 2, wherein the maximum voltage is between about 4.0 Vand about 5.0 V.
 12. The device according to claim 2, wherein the CCFlayer includes: a first sub-CCF layer for selectively reflecting lighthaving a wavelength range corresponding to one of a red, green, or bluecolor; and a second sub-CCF layer for selectively reflecting lighthaving a wavelength range corresponding to another one of a red, green,or blue color, different from the color selectively reflected by thefirst sub-CCF layer.
 13. The device according to claim 2, wherein thefirst transparent electrode includes a common electrode.
 14. The deviceaccording to claim 2, wherein the second transparent electrode includesa pixel electrode.